Casein kinase II is a highly conserved Ser/Thr protein kinase which is ubiquitous in eukaryotic organisms. The enzyme phosphorylates a broad spectrum of endogenous substrates, including several of the nuclear oncogene proteins. The activity is elevated in rapidly dividing normal cells, in transformed cells in culture, and in solid human tumors, and is stimulated following treatment of tissue culture cells with peptide growth factors. We have recently found that casein kinase II is essential for viability in S. cerevisiae and, furthermore, that inactivation of the enzyme leads to cell cycle arrest at two distinct points in the cell cycle, G1 and G2/M. A better understanding of this enzyme thus may provide important insights into normal cell cycle regulation, cell transformation, and cancer. The research proposed in this application is designed to elucidate the global physiological role of casein kinase II in a metazoan organism. The work makes use of Drosophila melanogaster as the experimental system because of its well characterized developmental biology and the potential for genetic analysis. The specific aims of the proposed research involve two broad areas: 1) structure/function studies and 2) physiological studies. The structure/function studies will be carried out in a recently developed expression system which makes use of S.cerevisiae as a host. Mutations in the alpha subunit will focus on residues likely to be involved i recognition of protein or nucleotide substrate and on conserved regions which may be involved in tetramer or filament formation; mutations in the beta subunit will address the role of the autophosphorylation reaction. Physiological studies will include localization of casein kinase II during early embryogenesis and construction of dominant, null, and temperature-sensitive mutations for analysis of function in vivo. The well characterized cell cycles of early Drosophila development will be exploited to determine whether casein kinase II is required for normal cell cycle progression, as it is in S.cerevisiae. Given the high degree of evolutionary conservation of the enzyme, the results should be broadly applicable to casein kinase II from higher organisms, including man.